Waves Waves transmit energy Some definitions Transverse waves

Waves

Waves transmit energy

Some definitions… Transverse waves are when the displacement is at right angles to the direction of the wave… Longitudinal waves are when the displacement is parallel to the direction of the wave…

Some definitions… Crest 1) Amplitude – this is “how high” the wave is: Trough 2) Wavelength ( ) – this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency – this is how many waves pass by every second and is measured in Hertz (Hz)

The Wave Equation The wave equation relates the speed of the wave to its frequency and wavelength: Wave speed (v) = frequency (f) x wavelength ( ) in m/s in Hz in m V f

Some example wave equation questions 1) A water wave has a frequency of 2 Hz and a wavelength of 0. 3 m. How fast is it moving? 2) A water wave travels through a pond with a speed of 1 m/s and a frequency of 5 Hz. What is the wavelength of the waves? 3) The speed of sound is 330 m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? 4) Purple light has a wavelength of around 6 x 10 -7 m and a frequency of 5 x 1014 Hz. What is the speed of purple light?

Reflection 13/02/202 2 Angle of incidence = Angle of reflection Normal Reflected ray Incident ray Angle of incidence Angle of reflection Plane mirror

How is an image formed? 13/02/202 2 Point object Virtual image Ray diagram to show image formation by a plane mirror The image is upright, virtual, the same size as the object and behind the mirror.

13/02/202 Refraction through a glass block 2 Wave slows down and bends towards the normal due to entering a more dense medium Wave slows down but is not bent, due to entering along the normal Wave speeds up and bends away from the normal due to entering a less dense medium

Diffraction 13/02/202 2 Diffraction is when waves spread out from the edge of a gap or around an obstacle. More diffraction if the size of the gap is similar to the wavelength If radio and TV signals do not diffract enough in hilly areas, reception will be poor.

Sound 13/02/2022 Sound is caused by mechanical vibrations, and travels as a longitudinal wave. Air molecules 1) An object makes a sound by vibrating 2) The vibrations pass through air by making air molecules vibrate 3) These vibrations are picked up by the ear

Sound facts 13/02/2022 Sound waves can travel through solids, liquids and gases. They generally travel fastest in solids and slowest in gases. Sound cannot travel through a vacuum. The human ear can hear frequencies between 20 Hz and 20, 000 Hz. The ability to hear higher frequencies declines with age. Sound waves can be reflected off hard surfaces (echoes), refracted and diffracted.

Musical sounds The pitch of a note depends on the frequency of the sound waves. The higher the frequency, the higher the pitch. The loudness of a sound depends on the amplitude of the sound waves. The greater the amplitude, the more energy the wave carries and the louder the sound. The quality of a note depends on the shape of the waveform. 13/02/2022

The electromagnetic spectrum Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: High frequency, _____ wavelength Gamma rays X-rays Low frequency, _____ (high) wavelength Ultra violet Visible light Infra red Microwaves Radio/TV γ Each of these types travels at the same speed through a _______ (300, 000 m/s), and different wavelengths are absorbed by different surfaces (e. g. infra red is absorbed very well by ______ surfaces). This absorption may heat the material up (like infra red and _______) or cause an alternating current (like in a __ _______). Words – black, microwaves, long, short, TV aerial, vacuum

Radio Waves Radio waves are used mainly for communications: Bluetooth headsets Cordless phones Freeview TV Wireless networks As far as we know, radio waves are harmless Radio signals

Radio Communications An alternating voltage applied to an aerial emits radio waves with the same frequency as the applied voltage. Waves received by an aerial produce an alternating current in the aerial with the same frequency as the received waves. The radio spectrum is divided into bands. The different bands are used for different purposes. The shorter the wavelength the more information the waves carry, the shorter their range and the less they diffract.

Microwaves Some microwavelengths are absorbed by water molecules and heat them up. If the water is in your cells, you might start to cook. Cooking Mobile phone networks use microwaves, and some people think that these could damage your health. There is no conclusive proof. Radar Satellite communications use microwaves. Radio waves are no good for this, as they are reflected by Earth’s atmosphere.

Infra-red is also called thermal (heat) radiation. Any conventional oven, toaster or heater uses infra-red. IR can cause burns. It is the IR in the Sun’s radiation that causes sunburn. IR is often used in optical fibres Remote controls

Visible Light This is the part of the electromagnetic spectrum that is detected by our eyes. We see the different wavelengths within it as different colours. Photography and film Optical fibres A mixture of all the colours in the visible spectrum gives white light.

Optical fibres An optical fibre is a long, thin, _______ rod made of glass or plastic. Visible or infra-red light is _______ reflected from one end to the other, making it possible to send ______ chunks of information. Optical fibres can be used for _____ by sending light coded with voice or data signals through the cable. The main advantages of this are reduced _______ loss, increased data capacity and improved _____. Words – communications, internally, security, large, transparent, signal